This application claims benefit of Japanese Patent Application No. 2002-011902 filed on Jan. 21, 2002, the contents of which are incorporated by the reference.
The present invention relates to optical units and, more particularly, to optical units utilized for cameras and the like.
Heretofore, so-called electronic cameras such as film cameras, electronic still cameras and video cameras have been put to practical use and widely spread, which are constructed such that, a foreground object image formed on the basis of a light flux of a foreground object (hereinafter referred to as foreground object flux) which is incident on an imaging optical system having a plurality of optical elements (or lens groups) and other elements, is focused on the light-receiving surface of a foreground object image obtaining means, such as a photographic imaging film or a charge coupled device (abbreviated CCD), disposed at a predetermined position, thereby obtaining a desired foreground object image and recording the same image in a predetermined form.
Such prior art film cameras and electronic cameras (both types of cameras being hereinafter generally referred to as cameras), are usually constructed to have an optical unit having an imaging optical system or an optical element (constituted by a plurality of lenses (hereinafter referred to as lens unit) for focusing the foreground object image on a predetermined position.
Usually, such a camera is brought outdoors by the user for use. Thus, importance has hitherto been attached to the portability of the cameras, and more and more thickness and size reduction of the camera itself has been demanded.
In recent years, electronic cameras which are constructed with a main aim of obtaining electronic still image data are being rapidly spread. Such electronic cameras usually comprise various constituent parts such as a circuit substrate, which is a member constituting part of a lens unit, and on which are mounted, for such purposes as zooming operation and focus adjusting operation, drive mechanism and actuators for causing movement of an optical element constituting an imaging optical system (hereinafter referred to as lens group) in predetermined directions as well as electric circuit for controlling these drive mechanisms and actuators.
This means that size reduction of the camera itself calls for adequately disposing constituent parts of the camera in the inside thereof while also taking the size reduction of the individual constituent parts into considerations.
As for lens units in prior art cameras, those of various forms are well known in the art, for instance one, in which in order to lead a foreground object light flux incident in the camera inside via a plurality of lens groups to a light-receiving surface of an imaging element or the like, a predetermined reflecting means such as a reflector or a prism is disposed in the optical path to let the optical path of the foreground object light flux be bent in a predetermined direction, for instance a direction substantially perpendicular to the incident light flux axis.
As the lens unit adopting so-called bending optical system as above, various proposals are made in various literatures such as Japanese Patent Laid-Open No. 2001-75162.
In the lens unit disclosed in the above Japanese Patent Laid-Open No. 2001-75162, a reflecting means for bending the optical axis of the foreground object light flux to a substantially perpendicular direction is disposed in the optical path of an imaging optical system, which transmits the foreground object light flux, thereby realizing size reduction of the electronic camera itself while securing an optical path length necessary for obtaining the image.
As shown, adopting the so-called bending optical system with a reflecting means or the like disposed in the optical path in the imaging optical system of electronic camera, can be thought to be very advantageous means for realizing the size reduction of the electronic camera itself.
In the meantime, in prior art cameras, wide use is made of small size stepping motors and DC motors (hereinafter merely referred to as small size motors) as actuators for individually driving respective lenses, which contribute to the zooming and focus adjusting operations, among the plurality of lenses constituting the imaging optical system.
However, when a usual actuator such as a small size motor is utilized for driving the lenses contributing to the zooming and focus adjusting operations, a problem is posed that a drive power transmitting mechanism for transmitting rotational drive power to the small motor is complicated.
Specifically, for carrying out the zooming and focus adjusting operations, predetermined lens groups have to be moved straight in directions among the optical axis of the imaging optical system. This means the need for a drive power transmitting mechanism for transmitting drive power from the small size motor as drive source to the zooming and focus adjusting lenses as driven members and also a drive power converting mechanism for converting the driving direction of the drive power.
The drive power transmitting and like mechanisms are usually constituted by gears. These gears or like constituent parts should be mechanically accurately manufactured to ensure reliable and loss-free drive power transmission to the driven members.
However, the camera which size reduction is demanded for, has a problem that accurate and inexpensive mass production is subject to difficulties. This means that for constructing a smaller size drive power transmitting mechanism, higher precision machining techniques are necessary, leading to the tendency of manufacturing cost increase.
Also, with the drive power transmitting or like mechanisms that are constructed with gears or the like, drive power is mechanically transmitted. Therefore, the drive power transmission is inevitably subject to drive power losses. Also, drive noise can not be perfectly suppressed.
Furthermore, in the usual camera, secondary batteries of low power capacity such as dry cells and lithium cells are usually used as the drive power supply. Saving of consumed power, is thus required for the electric constituent parts provided in the camera.
However, small size motors usually used as drive power supply of prior art cameras have a problem that high drive power is required. For example, small size motors usually used in cameras require power of 3 V/300 mA (i.e., roughly 1 W).
In prior art cameras, the control system of the camera is usually contrived such as to reduce the drive time of the small size motor for preventing wasteful power consumption. As an example, it is contrived to control the focus adjusting operation (i.e., AF operation) to be executed when and only when required at the time of imaging and also to control the focus adjusting and zooming operations such as not to be executed at the same time. Such controls tend to prolong the operation time as required for a series of imaging operations. This tendency leads to a problem of prolonging the time lag between the time when the shutter release button of the camera is actually operated by the user and the time when the shutter is actually driven for the exposure operation.
As shown above, in the case of utilizing the prior art small size motor or the like as the drive power supply (or actuator) in the camera, limitations are imposed on the size reduction and power saving of the camera.
In recent years, as the drive power source (or actuator) to be used in super-small size precision machines or the like, various types of actuator which are in different drive systems from the small size motor noted above are being developed.
For example, electrostriction actuators are described in xe2x80x9c2000 Micro-Machine Technique Research and Development (Power Generation Equipment High Performance Maintenance Technique Development) Commission Research Result Reportsxe2x80x9d, Foundation Micro-Machine Center, March, 2001.
FIG. 17 is a view schematically showing the construction of the electrostriction actuator described in the above literature.
As shown in FIG. 17, this electrostriction actuator 100 comprises a polymer thin film 101 and electrode layers 102 and 103 of a conductive material formed to be integral with the opposite surfaces of the polymer thin film 101.
The polymer thin layer 101 is a member of a soft material group capable of being readily deformed when experiencing external forces, such as silicone elastomer, acrylic elastomer and polyurethane.
The elastomer is the abbreviation of elastic polymer and refers to pronouncedly elastic polymers, i.e., polymer materials exhibiting rubber-like elasticity in the neighborhood of normal temperature or elastic materials having elongation rates of 100% and above. These materials have such a character that they are readily deformed by external forces but are restored to the initial form as soon as the external forces are removed.
The electrode layers 102 and 103 are made of carbon-containing grease or like materials, and when they are formed to be integral with the polymer thin layer 101, they can be deformed in the same direction as the direction of deformation of the polymer thin film 101.
In the electrostriction actuator 100 having the above structure, by applying a positive (or plus) voltage to the electrode layer 102 while applying a negative (or minus) voltage to the other electrode layer 103, the two electrode layers 102 and 103 exert pulling forces to each other (in the directions of arrows as shown in FIG. 17). As a result, the polymer thin layer 101 is deformed such as to be squeezed.
In this case, the polymer thin layer 101 itself, which is made of a soft material as noted above, is elongated in the directions of arrows Y in FIG. 17, i.e., the directions of its plane (i.e., horizontal direction).
When power supply to the two electrode layers 102 and 103 is turned off, the forces exerted to the polymer thin layer 101 in the directions of arrows X are removed, and the polymer thin layer 101 is thus restored to the initial form. Such characteristics are referred to as electrostriction effect, and the electrostriction actuator utilizes this electrostriction effect to generate drive power.
FIG. 18 is a graph showing the relation between the distortion caused by voltage application to the electrostriction actuator and the applied voltage. As shown in FIG. 18, the distortion (xcex94L/L0 (%)) has such a character that the actuator undergoes non-linear displacement in correspondence to given voltage E (V) and is restored to the initial form without generation of any hysteresis. Here, xcex94L represents the elongation of the electrostriction actuator, and Lo is the length dimension of the actuator in the directions of deformation (or elongation) without presence of any applied voltage.
The electrostriction actuator 100 as described, which generates drive power by deforming itself, does not require any complicated drive power transmitting mechanism, and can provide desired drive power with a very small size and simple structure compared to the prior art small size motor or like actuator. Besides, without need of any drive power transmitting mechanism such as gears, the electrostriction actuator can realize power saving and noise reduction.
The present invention was made in view of the above points, and its object is to provide an optical unit, which uses, in view of small size motors or actuators usually utilized in prior art cameras or the like, electrostriction actuators utilizing the electrostriction effect, thus simplifying drive power transmitting and like mechanisms and permitting contribution to its size reduction ad power saving.
Aspects of the present invention are summarized in the following with reference to member or component attached with numerals in the drawings. These concrete indications merely refer to clarify the example of structure and does not limit any scope of the present invention.
According to an aspect of the present invention, there is provided an optical unit comprising: a plurality of lens support members (lens frames 23 and 24) each holding a lens capable of being driven for displacement in unison with the lens for desired optical adjustment; a guide bar (main guide bar 26) for restricting the lens support members such that the displaceable direction thereof is along a predetermined direction; and a plurality of actuator elements (refers to FIGS. 5 to 7) each including a curved plate-like electrostriction element (actuators 33 and 36) of a polymer material layer laminate disposed curvedly along and in a state of being wound on part of the outer periphery of the guide bar for generating a drive displacement such as to be expansion or compressed in the longitudinal direction of the guide bar in response to a drive voltage applied across itself (voltage control or application and removal of the voltage), the drive displacement being capable of being transferred to the lens support member.
Each electrostriction element in each actuator element is a substantially hollow cylindrical member in form and has a release part formed on part of the own outer periphery along the axial direction.
Each actuator element further includes a biasing element (note: spring element in the additional figure (FIG. 7(b)) for providing a pre-strain (preliminarily given strain) to the curved plate-like element to cause strain thereof in curved circumferential direction.
The biasing element is an elastic member (i.e., spring element in FIG. 7(b)) for providing a stress in the curved plate-like electrostriction element in a direction of causing expansion of the electrostriction element by generating a biasing force in a direction to cause compression of itself at all times.
The electrostriction element of the actuator element is substantially cylindrical in form and has a release part formed on part of the outer periphery of itself and extending in the axial direction, the release part further including a biasing element for providing a pre-strain for causing expansion of the electrostriction element in the curved circumferential direction.
The elastic member is a curved plate-like spring, which is saw-wave like in form and extends in the axial direction perpendicular to the direction of action to the own bias force.
The actuator element includes a cover member (38 in FIGS. 5 to 7) provided on the side of the outer periphery of the curved plate-like electrostriction element.
The actuator element includes a cover member (cover member in FIG. 7(b)) provided on the side of the outer periphery of the biasing element.
The curved plate-like electrostriction element has one axial end in contact with a stationary part at all times, and when it undergoes strain or expansion displacement as a result of application of a drive voltage across it, its other end is brought into contact with the corresponding lens support member to push and cause displacement of the lens support member.
The actuator element is constituted by a plurality of actuators each provided for a corresponding one of lens support members.
Other objects and features will be clarified from the following description with reference to attached drawings.